CD-ROM with machine-readable I.D. code

ABSTRACT

A machine-readable serial number is formed on a CD-ROM by using a laser to selectively remove a reflective layer from the CD-ROM. Removal of the reflective layer creates defects in addressable information storage locations on the CD-ROM. The serial number is read by detecting the defects. The serial number is used in a software distribution system in which many different software programs are distributed on a single CD-ROM and an access code based on the desired software program and the serial number of a particular CD-ROM is used to &#34;unlock&#34; the desired program on the particular CD-ROM.

This application is a division of application Ser. No. 08/346,423, filedNov. 29, 1994, which is a division of application Ser. No. 08/132,709,filed Oct. 6, 1993 now U.S. Pat. No. 5,400,319.

FIELD OF THE INVENTION

This invention relates to optical information storage disks, and moreparticularly, to providing a machine-readable serial number code on suchdisks.

BACKGROUND OF THE INVENTION

It has been proposed to increase efficiency in the distribution ofcomputer software by distributing many software programs on a singleCD-ROM instead of distributing each program on a separate floppy disk orset of floppy disks. In this proposed distribution system, a customerwho has the CD-ROM (hereinafter sometimes referred to as "the disk") inhis possession and desires to obtain access to one of the programs onthe disk purchases an access code which may be used to gain access tothe desired program.

In order to carry out this software distribution system, it is desirableto provide a serial number or identification number on the disk inmachine-readable form so that access codes can, through encryption, belimited to use with only one disk serial number, thereby preventingunauthorized use of the access code on more than one disk. However, themost efficient manner of producing CD-ROMs is by molding each disk froma master, which results in each disk containing identical recordedinformation. In other words, if a conventional mastering process is usedto record a "serial" number on the disk, each disk formed from a givenmaster will have the same "serial" number. It has been proposed to useapproximately 20 different masters to produce compact disks whichcontain identical software program information, with each masterrespectively used to produce disks having an identification number thatis different from the identification numbers of disks produced usingdifferent masters. However, this approach suffers from two drawbacks:First, the cost of mastering is significantly increased, and secondly,the number of different disk identification numbers is the same as thenumber of different masters, i.e. about 20, which makes it relativelyeasy for unscrupulous persons to locate disks having the sameidentification number and then to use a single access code to "unlock"the same program on all of the disks which have the same identificationcode.

It is also possible to use disk manufacturing processes without moldingfrom a master, with a unique serial number being recorded on each diskat the same time the program software is recorded, for example bymagneto-optical recording, but such processes are substantially moreexpensive than molding CD-ROMs from a master.

Another constraint on provision of serial numbers on CD-ROMs is the needfor the serial number to be readable using conventional hardware such asgenerally available CD-ROM drives interfaced to personal computers.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of manufacturing an optical information storage disk having amachine-readable identification number, in which each disk whichcontains the same program information is formed by molding with the samemaster.

It is another object of the present invention that a large number ofdifferent identification numbers be provided on the respective disks.

It is still another object of the invention that the disk identificationnumber be readable using conventional personal computer peripheralhardware.

In accordance with the invention, there is provided a method of forminga machine-readable code on an optical disk including the steps offorming a disk-shaped molded substrate which includes an informationrecording area in which information is represented by pits formed in theinformation recording area, applying a reflective coating to theinformation recording area, and removing the reflective coating fromselected portions of the information recording area to form a codepattern.

According to another aspect of the invention, there is provided anapparatus for forming a machine-readable code pattern on a pre-recordedcompact disk that includes a reflective coating on an informationbearing substrate, the apparatus including means for rotating the diskabout a center of rotation of the disk, a laser for selectively emittinga cutting beam, means for directing the cutting beam to a point at aselected distance from the center of rotation of the disk, and means forcontrolling the laser and the means for directing so that the reflectivecoating is removed from selected portions of the information bearingsubstrate to form the machine-readable code pattern.

According to still another aspect of the invention, there is provided anoptical information storage disk in which a reflective coating is formedon a molded information bearing substrate and wherein the reflectivecoating is removed in a predetermined pattern from selected portions ofthe substrate to form a machine-readable code.

According to yet another aspect of the invention, there is provided amethod of applying a human-readable serial number to an opticalinformation storage disk having a machine-readable code formed thereon,the method including the steps of reading the machine-readable codeformed on the disk, performing an encryption algorithm with respect tothe machine-readable code to obtain an encrypted code, and applying theencrypted code to the disk in human-readable form.

According to a further aspect of the invention, there is provided amethod of forming a machine-readable code on an optical informationstorage disk including the steps of forming a plurality of addressableinformation storage locations on the disk, with at least some of thestorage locations containing program information, and creating defectsin some of the information storage locations in a predetermined patternso as to form a machine-readable code.

According to still a further aspect of the invention, there is provideda method of providing access to a selected one of a plurality ofsoftware programs stored in a CD-ROM, including the steps of insertingthe CD-ROM into a CD-ROM drive interfaced to a personal computer,entering into the personal computer an access code for providing accessto the selected one of the plurality of software programs, examining aplurality of information storage locations on the CD-ROM to detectdefects in the information storage locations, establishing a diskidentification code on the basis of results of examining the pluralityof information storage locations, and verifying the entered access codeon the basis of the established disk identification code.

By providing the methods and apparatus described above, a large numberof software programs can be distributed on a single CD-ROM, using accesscodes for accessing each of the programs on the CD-ROM, with the codesbeing formed on the basis of serial numbers that are, for practicalpurposes, unique to each respective CD-ROM. Each CD-ROM which is toinclude identical information content can be formed using the samemaster, with the substantially unique serial number being formed on thedisk after mastering and at a relatively low cost. Software provided inaccordance with the invention allows the serial numbers to be read byconventional hardware including a standard PC connected to aconventional CD-ROM drive.

The above, and other objects, features and advantages of the presentinvention will be apparent from the following detailed descriptionthereof which is to be read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a CD-ROM having amachine-readable code pattern formed thereon in accordance with thepresent invention;

FIG. 2A is a block diagram of an apparatus for forming amachine-readable code pattern on a CD-ROM;

FIG. 2B is a block diagram of an alternative embodiment of an apparatusfor forming a machine-readable code pattern on a CD-ROM;

FIG. 3 is an illustration of a band format used for forming amachine-readable code on a CD-ROM in accordance with a preferredembodiment of the invention;

FIG. 4 is a block diagram of an apparatus for reading a machine-readablecode pattern from a CD-ROM and applying a human-readable serial numberto the CD-ROM, in accordance with the present invention;

FIG. 5 is a schematic illustration of computer hardware in which aCD-ROM is loaded for controllably accessing software packages stored onthe CD-ROM in accordance with the present invention;

FIG. 6 is a flow chart which illustrates a software routine forcontrollably accessing a software package stored on a CD-ROM inaccordance with the present invention; and

FIG. 7 is a flow chart which illustrates a subroutine for reading an IDcode from a CD-ROM, and which is part of the routine illustrated in FIG.6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will first be described, with reference to FIGS. 1A and 1B, anoptical recording disk having a machine-readable code pattern formedthereon in accordance with the present invention.

In FIG. 1, reference numeral 10 indicates an optical recording disk. Thedisk 10 is, except for the machine-readable code pattern and the codepattern area to be described below, preferably a conventional CD-ROMwhich is used for storing computer programs, digital data and the likefor reproduction by a conventional CD-ROM drive provided as a peripheraldevice in a personal computer system.

The surface of the disk 10 is divided into a circular hub area 12, arelatively wide annular program or information storage area 14 thatsurrounds and is concentric with the hub area 12, and an outer mirrorarea 16 in the form of a rather narrow ring surrounding the program area14. A circular boundary 18 is formed where the program area 14 meets themirror area 16.

The CD-ROM 10 is preferably of the type, well known to those skilled inthe art, which is manufactured by molding a polycarbonate disk-shapedsubstrate with a master to form a pattern of information storage bits inthe program area 14. After molding, a reflective aluminum coating isapplied to the polycarbonate substrate and then a protective layer oftransparent ink is formed on top of the reflective coating.

The pits which represent the stored information are arranged in spiralor concentric tracks with a track pitch that is typically about 1.6microns. Storage location addressing information or the like is arrangedat regular intervals along the tracks.

In accordance with the invention, the program area 14 includes a codepattern area 20 near or adjacent to the boundary 18 between the programarea 14 and the mirror area 16. A machine-readable code pattern 22 isformed in the code pattern area 20.

As best seen in FIG. 1B, the code pattern 22 is formed by a plurality ofcode pattern bands 24 which extend in parallel to each other in thecircumferential direction of the disk 10. The code pattern bands areformed by removing the aluminum coating from the program area 14 at theplaces indicated by the bands 24, according to a method to be describedbelow. The bands 24 are, in a preferred embodiment, rather narrow,having a width (in the radial direction of the disk 10) of approximately25 microns. Preferably all of the bands 24 are of substantially the samewidth. The length of the bands 24 (in the circumferential direction ofthe disk 10) is determined in accordance with what is required forreliable reading of the code pattern by methods to be described below.In a preferred embodiment of the invention, the length of the bands 24is around 5 to 10 millimeters.

The code pattern 22 illustrated in FIG. 1B represents a seven digitbinary code in which the presence of a band in a particular location(i.e., the absence of the reflective coating at that location) is takento represent the value "1", whereas the absence of the band (i.e., thepresence of the reflective coating) at such a location is taken torepresent the value "0". (It will be appreciated that the oppositeconvention could be used, in which the presence of a band was accordedthe value "0", and the absence of the band was considered to indicate a"1".) Also, according to the convention to be used in the example ofFIG. 1B, the bands are read proceeding radially outwardly from theinnermost band. Thus, the code pattern 22 of FIG. 1D represents thebinary number "1101101" (that is, 109 in decimal numerals), with the twoinnermost bands each respectively representing a "1" and being followedby a gap representing a "0", which is in turn followed by two bandsrepresenting "1"s, followed again by a gap for a "0" and concluding withan outermost band representing the final "1".

It will be recognized that by using a seven-bit code pattern as shown inFIG. 1B, up to 128 distinct machine-readable ID codes may be formed.However, it is within the contemplation of the invention to provide alarger number of distinct ID codes, utilizing eight or more binary bits,and in a preferred embodiment a sixteen-bit binary code is used.

FIG. 2 illustrates in block diagram form an apparatus 100 used forforming a machine-readable code pattern on a CD-ROM in accordance withthe present invention.

Major portions of the apparatus 100 include a control and displaysection 102, an optical section 104 and a signal processing section 106.The apparatus 100 also includes a turntable 108 for receiving thereonand rotating a disk 10.

The control and display section 102 includes a motor 110 which isconnected via a connecting mechanism 112 for controllably rotating theturntable 108 and the disk 10. The control and display section 102 alsoincludes a control system 114 which is connected for controlling motor110.

The control system 114 also performs a number of other functions, asdescribed below, and preferably includes a conventional personalcomputer or the like, including a display 116 and a keyboard 118, bywhich a user interface is provided.

The optical section 104 includes a laser 120, which is preferably aconventional medium power device of the type designed formicro-machining, such as a Nd:YAG laser. The laser 120 emits a beam 122that is adjustably directed via a beam deflector 124 and a lens systemL1 onto the program area 14 of the disk 10. The laser 120 is selected,and the lens system L1 is arranged, so that the beam is focused on thesurface of the program area 14 in a spot having a diameter of about 25microns, and with sufficient power to vaporize the aluminum coating. Thebeam deflector 124 is selectively movable in directions indicated byarrows A for adjusting the point on the surface of disk 10 to which thefocused beam 122 is directed. In a preferred embodiment of the inventionthe point of focus of beam 122 is adjustable among selected radialpositions relative to a center of rotation of the disk 10. In otherwords, the axis along which the focused beam may be deflected preferablycoincides with a radius of the disk 10.

The beam deflector 124 may take the form of a rotating mirror, anacousto-optic modulator, or a low-inertia scanning device such as agalvanometer.

The optical section 104 further includes a laser power control andmodulation circuit 126, which provides on/off control, power levelcontrol and modulation of laser 120. The laser control circuit 126 isconnected to receive control signals from control system 114 of controland display section 102.

As will be seen, the apparatus 100 is operable in a "read back" mode,and for this purpose a read back detector 128 and a beam splitter 130are provided. The beam splitter 130 is positioned so as to direct toread back detector 128 a reflected beam 122' that is reflected back fromthe surface of disk 10 via the beam deflector 124.

Also included in the optical section 104 is an eccentricity compensator132. As will be described below, the eccentricity compensator 132cooperates with the control system 114 to provide precise positioning ofthe focused beam 122 on the surface of disk 10 relative to theprogram/mirror boundary 18.

The eccentricity compensator 132 includes a laser diode 134, a beamsplitter 136, a lens system L2 and a photo detector 138. As will bediscussed in more detail below, a beam 140 emitted by laser diode 134 isdirected by beam splitter 136 and lens L2 to the nominal position of theboundary 18 on the surface of disk 10 and the beam 140 is reflected backfrom the surface of disk 10 to the photo detector 138. Although notshown in the drawing, it should be understood that a signal path isprovided between the control system 114 and the laser diode 134 foron/off control of laser diode 134 by the control system 114.

The signal processing section 106 includes a signal conditioning andprocessing circuit 142, a deflector driving circuit 144 and a signalconditioning circuit 146. The signal conditioning and processing circuit142 is connected to receive an output signal from the read back detector128. The signal conditioning and process circuit 142 conditions andprocesses the detector output signal and provides a detection signal tothe control system 114.

The deflector driving circuit 144 provides a driving signal to the beamdeflector 124 for the purpose of controlling the positioning of the beamdeflector 124 (and hence also the focusing point of the beam 122 withrespect to the surface of the disk 10). The driving signal output fromthe deflector driving circuit 144 is based upon two input signalsprovided to the driving circuit 144. The first of the input signals is aradial position control signal provided from the control system 114, andis indicative of a selected radial position on the disk 10 to which thebeam 122 is to be directed. As will be seen, in a preferred embodimentof the invention, the signal provided from the control system 114 to thedriving circuit 144 is such as is required to direct the beam 120 to aselected one of 16 different radial positions relative to the center ofrotation of the disk 10.

The other input signal received by the driving circuit 144 is acompensation signal provided from signal conditioning circuit 146. Thesignal conditioning circuit 146 is connected to receive an output signalprovided from the photodetector 138 of the eccentricity compensator 132.Because all CD-ROM's are eccentric to some extent, it is necessary toprovide eccentricity compensation to achieve the desired accuracy informing the code pattern on the disk 10.

As will be described in more detail below, the photodetector 138 outputsa signal indicative of the degree of eccentricity of the disk 10. Thesignal output from the photodetector 138 is conditioned by signalconditioning circuit 146 to provide a compensation signal which is addedat the driving circuit 144 to the radial position control circuitprovided by the control system 114. As a result, the output signal fromthe driving circuit 144 provides desired radial positioning of the beam122 on the surface of the disk 10, with compensation for theeccentricity of the disk 10.

In operation, a disk 10 which has been molded to form the informationbearing pits in the aforementioned track arrangement, with the aluminumreflective coating having been applied to the molded substrate, isplaced on the turntable 108 of the apparatus 100. Via the keyboard 118an operator enters a command to start the process of forming themachine-readable code pattern and the control system 114 determines aserial number that is to be applied to the disk 10. For example, aserial number applied to an immediately preceding disk may beincremented to generate the serial number to be applied to the presentdisk 10. The serial number is either generated in binary form or isconverted to binary form by the control system 114.

The apparatus then proceeds to form the code pattern 22 on the disk 10by removing the reflective coating band by band with respect to thebinary digits having the value "1" in the serial number to be applied tothe disk. Before forming the first band, the disk 10 is rotated aninitial time by means of turntable 108 and motor 110, and during theinitial rotation of the disk the eccentricity compensator 132 isoperated in a calibration mode. More specifically, the laser diode 134is turned on, and the beam 140 emitted by the laser 134 is directed viathe splitter 136 and the lens L2 onto a location on the surface of disk10 that is selected to be the nominal position of the program/mirrorboundary 18. The beam 140 is reflected back from the surface of disk 10through the beam splitter 136 to the photodetector 138, which outputs asignal that represents the intensity of the reflected beam at thephotodetector 138. Because disk 10 is eccentric, and the mirror area 16is more reflective than the program area 14, the intensity of thereflected beam fluctuates over the period of rotation of the disk 10,and the output signal of the photodetector 138 fluctuates accordingly.The slope of the fluctuation indicates the phase and the degree of theeccentricity, and is used at the signal conditioning circuit 146 to forma compensation signal which compensates for the eccentricity in the disk10.

The initial rotational period of the disk 10 also allows the operationof the turntable 108 and the control and display section 102 to becomestabilized.

On the second rotation of the disk 10, the control system 114 outputs aradial position control signal to drive the beam deflector 124 to anappropriate position for directing the beam 122 of the laser 120 to aradial position on the disk 10 that corresponds to the first "1" bit ofthe binary serial number. The radial position control signal output fromthe control system 114 is provided to the deflector driving circuit 144,which adds the compensation signal from the signal conditioning circuit146 and the radial position control signal from the control system 114to form a driving signal that appropriately positions the beam deflector124 to direct the beam 122 to the desired radial location on the disk10, taking into account the eccentricity of the disk 10.

After the positioning of the beam deflector as just described, andduring the second rotation of the disk, the control system 114 outputs asignal to the laser control circuit 126, which in turn drives the laser120 so that it emits a beam 122 at a sufficient intensity to form a bandin which the reflective coating is removed and for a predeterminedperiod of time that is sufficiently long to form the band in a desiredlength, which may be from 5-10 mm, for example. At the end of thepredetermined time, the laser beam 122 is turned off.

During the period in which the beam 122 is forming the first band, theradial position control signal remains constant, but the compensationsignal from the signal conditioning circuit may be changed to compensatefor eccentricity in the disk 10, so that the position of beam deflector124 is adjusted to maintain the beam 122 at the desired radial positionon the surface of disk 10 relative to the boundary 18.

During the next (i.e., the third) rotation of the disk, the controlsystem outputs another radial position control signal to reposition thebeam deflector so that the beam 122 will be directed to a radialposition corresponding to the band for the next "1" bit. Again the beam122 is turned on for the predetermined time period to form a band of thedesired length. The time at which the beam is initially turned on tostart forming the next band is controlled by the control system 114 tobe substantially one period of rotation of the disk after the time atwhich the beam 122 was initially turned on to form the first band. Thetiming may be established by control system 114 on the basis of a knownperiod of rotation of turntable 108, or alternatively may be based uponcode pulses provided from an encoder (not separately shown) associatedwith motor 110.

Each of the bands corresponding to the remaining "1" bits of the binaryserial number is formed in the manner just described. It will beunderstood that the period of the laser "burn" for forming each band iscommenced at substantially the same phase of rotation of the disk 10,and continues for the same amount of time, so as to produce the codepattern 22 confined to the code pattern area 20 as shown in FIG. 1B.

Although the bands are shown in FIG. 1B as being substantiallycontinuous, it should be noted that such bands could be produced byrapid pulsing of the engraving beam 122 as well as by continuousapplication thereof. Moreover, it is also within the contemplation ofthe invention that the bands consist of discrete engraved spots, whichcould be produced by pulsing the beam 122 less rapidly than a pulsingrate which produces continuous bands.

After the formation of the code pattern bands has been completed, theapparatus 100 preferably proceeds to a "read after write" mode, in whichthe satisfactory formation of the code pattern is checked. In this mode,the control system 114 sequentially controls the beam deflector 124 todeflect the beam 122 to positions corresponding to each of the 16potential band locations and while the beam deflector is positioned foreach potential band location, the control circuit 114 causes the disk 10to be rotated through one or more rotations, while controlling the laser120 to output a beam 122 in a relatively low power continuous wave mode.The low power beam 122 is directed to the particular potential bandposition by the deflector 124, with compensation for the disk'seccentricity, and is reflected from the surface of the disk 10 to form areflected beam 122' which is directed to the read back detector 128 toprovide a signal level indicative of whether the reflective coating ispresent or absent at the radial position on the disk 10 to which thebeam 122 is directed. The output signal from the read back detector 128is conditioned and processed by the signal conditioning and processingcircuit 142 and the resulting signal is output to the control system114. In this way the apparatus 100 "reads" each of the 16 potential bandlocations to determine for each location whether or not a bandrepresenting a "1" bit is present. The apparatus then compares theresult of the reading to the binary number which was to be applied todisk 10 to confirm that the code pattern was properly formed.

If the read back process fails to confirm that the code pattern wasproperly formed, then appropriate action is taken, such as discardingthe disk. Otherwise, if the formation of the proper code pattern isconfirmed, the disk manufacturing process proceeds to completion.

An alternative approach to forming the code pattern shown in FIG. 1B isembodied in an apparatus 100' illustrated in block diagram form on FIG.2B. Elements shown in FIG. 2B which correspond to the elements of FIG.2A are given like reference numerals and will not be described indetail. Like the apparatus 100 shown in FIG. 2A, the apparatus 100' ofFIG. 2B has a turntable 108 for rotating the disk 10, a control anddisplay section 102, and an engraving laser 120' with its associatedlaser control circuit 126.

The apparatus 100' also includes a rotating mirror assembly 160 whichfunctions as a beam deflector, and which, together with lens system L1,selectively directs the beam 122 from engraving laser 120' to desiredradial positions on the surface of the disk 10. The rotating mirrorassembly 160 includes a motor (not separately shown) for rotationallydriving the mirror assembly 160 and an encoder 162 associated with themotor for providing encoder pulses to the system 114.

The eccentricity compensation function of the apparatus 100 (FIG. 2A) isperformed in a different manner by the apparatus 100'. Morespecifically, the laser beam 140 produced by laser diode 134 and usedfor eccentricity compensation in the apparatus 100' (FIG. 2B) isdirected to varying radial positions on the disk 10 by the rotatingmirror 160 and lens L1 in a similar manner to the beam 122 of theengraving laser 120'. The optical path for the beam 140 from the laserdiode 134 to the rotating mirror 160 includes a polarized beam splitter164, a quarter wave plate 166, and a dichromatic mirror 168. Thedichromatic mirror 168 is selected so as to be highly reflective at thewavelength of the beam 140 and highly transmissive at the wavelength ofthe beam 122. A return path for a beam 140' produced by reflection ofthe beam 140 from the disk 10 is provided via the lens L1, the rotatingmirror 160, the dichromatic mirror 168, the quarter wave plate 166 andthe polarized beam splitter 164, so that the reflected beam 140' isdirected to a read back detector 138'. A signal output from the readback detector 138' is provided to a signal conditioning and processingcircuit 146', which provides a detection signal to the control system114.

The control system 114 is connected through signal paths which are notshown in the drawing to provide on/off control of the laser diode 134and of the motor for the rotating mirror assembly 160.

In operation, a binary serial number to be applied in machine-readableform to the disk 10 is generated in the same manner as in the apparatus100 of FIG. 2A. However, in the apparatus 100' (FIG. 2B) no initializingrotation of the disk 10 is required. Rather, with the disk 10 at rest inan arbitrary rotational position, the laser diode 134 and the motor inthe rotating mirror assembly 160 are both turned on, with the rotatingmirror assembly 160 being continually rotated at a constant rotationalspeed and the laser diode remaining on throughout the code patternengraving operation now being described. The beam 140 emitted by thelaser diode 134 is directed via the beam splitter 164, the quarter waveplate 166 and the dichromatic mirror 168 for reflection by the rotatingmirror 160. Depending upon the instantaneous rotational position of therotating mirror 160, the beam 140 may or may not be reflected from thesurface of the disk 10 so that it is directed back to the read backdetector 138'. Moreover, the rotating mirror assembly 160 is positionedwith respect to the program/mirror boundary 18 of the disk 10 such thatat some rotational positions of the mirror 160 a reflected beam 140' isreturned from the mirror area 16 of the disk 10, and at other rotationalpositions of the mirror 160, the reflected beam 140' is returned fromthe program area 14 of the disk 10.

The output signal of the read back detector 138' and the conditioneddetection signal by the signal conditioning and processing circuit 146'are indicative of the intensity of light incident upon the read backdetector 138'. The intensity of light incident on the read back detector138' is at a low level at times when the rotational position of themirror 160 prevents the reflected beam 140' from reaching the read backdetector 138'. The intensity of the light incident upon the read backdetector 138' is at a high level when the beam 140' is returned to theread back detector 138' from the highly reflective mirror area 16, andthe intensity is at an intermediate level when the beam 140' is returnedfrom the moderately reflective program area 14. Accordingly, thedetection signal provided from the conditioning and processing circuit146' to the control system 114 is at one of three levels, namely a lowlevel indicative of no beam return, a high level indicative of beamreturn from the mirror area 16, and an intermediate level indicative ofa beam return from the program area 14. With constant rotation of therotating mirror 160 in the direction indicated by the arrow Ro, the pathof the beam 140 is continually changed from the rotating mirror 160onward along an axis that substantially coincides with a radius of thedisk 10. When the beam is incident upon the rotating mirror 160 at arather acute angle, no reflected beam 140' is present at the read backdetector 138', with the beam 140 being deflected to a position outboardfrom the disk 10. But with continued rotation of the mirror 160 the beam140 is directed radially inwardly onto and across the mirror area 16,past the boundary 18 and on to the program area 14. Accordingly, theintensity of light incident on the read back detector 138' varies overtime from a low level to a high level to an intermediate level duringthe progressive deflection of the beam 140 in a radially inward manneras just described. At the same times, respective signals indicative ofthe low, high and intermediate detected intensities are provided tocontrol system 114. In particular, the control system 114 is adapted tonote the transition from high intensity to intermediate intensity, whichindicates the point in time at which the beam path is deflected acrossthe program/mirror boundary 18. The time at which the deflected beam 140crosses the boundary 18 is then used as a benchmark for code patternengraving using the laser 120', so that the code pattern bands can beformed at a fixed distance from the boundary 18, notwithstandingeccentricity in the disk 10. It will be noted that this is possiblebecause the engraving beam 122 shares the same beam deflection path withthe eccentricity compensation beam 140.

Accordingly, at a predetermined time interval after the beam pathcrosses the boundary 18, the control system 114 causes the laser 120' toemit one or more intense pulses of the engraving beam 122 so as to forman engraved spot on disk 10 from which the reflective coating isremoved. The predetermined delay period between when the beam crossesthe boundary 18 and the time at which the laser 120' is actuated to formthe engraved spot is selected so that the spot is formed in the codepattern band location which corresponds to the first "1" bit in thebinary serial number to be applied to the disk 10. Then, after anotherpredetermined delay, the laser 120' is again operated to engrave anotherspot at the radial location corresponding to the band for the next "1"bit in the serial number. This process continues during the samedeflection pass of the beam path so that a respective spot is formed foreach of the bands required for the "1" bits of the serial number.Although formation of all of the required spots in a single deflectionpass is preferred, it is also contemplated that multiple passes, up toone deflection pass per spot, could be performed to engrave all of therequired spots along a single radius of the disk 10 (i.e., at the samerotational position of the disk 10). The timing for establishing thedelay periods after which engraved spots are formed may be based on atiming circuit within control system 114 or upon code pulses supplied tocontrol system 114 from encoder 162.

After the respective spots have been formed at each of the "1" bitpositions, the control system 114 outputs a signal to the motor 110 sothat the disk 10 is rotated a very small distance by the turntable 108.The rotation is such that the radius along which the spots were justformed is at a very small angle to the disk radius which, after therotation, coincides with the axis of deflection of the beam. Forexample, at the radial positions of the disk 10 at which the spots wereformed, the displacement between the radius upon which engraving wasjust performed and the radius now coinciding with the beam deflectionpath may be in the range of 5 to 100 microns, or more.

After the small rotation of the disk, another set of spots correspondingto the "1" bit locations is then engraved along the new radius in thesame manner as just described (i.e., at the same time delays after thebeam deflection path crosses the boundary 18), and the disk is thenrotated again by the same small amount and the process is repeated untilbands of the desired length have been formed. With an engraved spotdiameter of approximately 25 microns, it will be appreciated that asubstantially continuous band is formed if the intermittent rotationbetween engraving operations is in the lower end of the 5-100 micronrange mentioned above, whereas with rotation within or beyond the upperend of the range, bands consisting of discrete spots will be formed.

The number of radii of the disk along which spots are formed depends onthe desired density of the spots and the desired length of the bands.For example, the number of radii may be 50 or more, which implies that50 or more radial passes of the engraving beam are carried out.

It should be noted that in the beam path provided for the eccentricitycompensation beam 140, the quarter wave plate 166 increases theintensity of the reflected beam 140' at the read back detector 138' bychanging the linear polarization of the outward bound beam 140 to acircular polarization and by changing the resulting circularpolarization of the reflected beam back to a linear polarization in thereturn path of the reflected beam 140'. However, the quarter wave plate166 can be dispensed with if the laser diode 134 is selected to have amore powerful output beam and/or more sensitive detection circuitry isprovided.

With the arrangement as shown in FIG. 2B, a relatively inexpensiveNd:YAG laser, operable only in a pulsed mode, can be used. However, itis within the contemplation of the invention to substitute a moreexpensive Nd:YAG laser, which is operable in a continuous wave mode aswell as a pulsed mode. With such an Nd:YAG laser, the laser diode 134and the quarter wave plate 166 can both be dispensed with, and theNd:YAG can be operated in a low power continuous wave mode to providethe reflected beam used for detecting the time at which the beam pathcrosses the boundary 18 on the disk 10.

According to alternative embodiments of the invention, the formation ofthe code pattern by vaporizing selected portions of the aluminumreflective coating is performed either before or after application ofthe transparent protective ink layer over the aluminum reflectivecoating. If the vaporizing of the reflective coating is performed afterthe protective layer has been applied, then the protective layer isvaporized along with the reflective coating, but residual heat afterremoval of the laser beam causes the protective layer to flow fromadjacent areas to cover the locations from which the material wasvaporized, so that the protective layer is reformed over the bandsremoved from the reflective coating.

FIG. 3 illustrates additional details concerning the format in which thecode pattern bands are formed. As mentioned before, in a preferredembodiment of the invention a 16 bit machine-readable code is to beformed so that 16 bands 150-1, 150-2, . . . , 150-16 are provided,respectively corresponding to 16 bit locations. The bands 150-1-150-16are arranged one after the other, proceeding radially inwardly from aprogram read out area 152.

It should be understood that FIG. 3 is presented on a scale such thatthe curvature of the bands 150 is negligible, and the bands 150 arepresented as being parallel in the circumferential direction of the disk10, which is indicated by the arrows C. Also, only a small portion ofthese bands 150 is shown in FIG. 3, inasmuch as the band format extendsaround the entire circumference of the disk 10. The width of each band150 (i.e., its dimension in the radial direction indicated by the arrowsR) is approximately 100 microns. Thus all 16 of the bands 150 togethermake up an annular region of the program area 14 having a width of about1.6 mm. Each of the bands 150 is divided approximately evenly in thecircumferential direction to form an engraving sub band 154 and aninformation sub band 156, each having a width of about 50 microns.

Each engraving sub-band 154 is in turn divided into an engraving area157 between safety areas 158. The engraving areas 157 and safety areas158 extend in the circumferential direction of the disk 10 and theengraving areas have a width (i.e. a dimension in the radial direction)of about 25 microns, with each of the safety areas having a width ofabout 15 microns. If an engraved band representing a value "1" is to beformed with respect to a particular bit, the engraving is performedwithin the engraving area 157 of the band 150 which corresponds to thatbit. The safety areas 158 are provided as buffers in case of mechanicalinstability or the like during engraving. The information sub-bands 156are kept free of engraving whether or not the respective bit is to havea value "0" or "1". In this way, track addressing information will bepreserved in the information sub-bands 156 to facilitate the codereading operation which will be described below. These areas may also beused to store special instructions for the CD player, software versionnumbers and the like. Alternatively, some or all of the informationsub-bands 156 may be allocated as additional potential bit locations, toincrease the number of bits in the code.

It is also contemplated to modify the format of FIG. 3 by, for example,increasing the width of one or more of the engraving sub bands 154 orinformation sub bands 156. For instance, the information sub bands ofthe last two bands 150 may be increased in width to about 200 micronseach.

There will now be described a method by which a human-readable serialnumber is applied to a disk 10 upon which a machine readable code hasbeen applied as previously described. Referring to FIG. 4, an apparatus200 for applying a human-readable serial number is shown in schematicform. The apparatus 200 includes a reading optics section 202, anengraving optics section 204, a reading control/data acquisition andprocessing section 206 and an engraving control section 208. Althoughnot explicitly shown in FIG. 4, it will be understood that the apparatus200 also preferably includes a turntable or the like for rotating thedisk 10.

Apparatus 200 may operate to read the machine-readable code pattern in amanner similar to the read-after-write mode of operation of theapparatus 100 shown in FIG. 2A. Accordingly, the reading optics section202 may be embodied substantially in accordance with the optical section104 shown in FIG. 2A, except that the Nd:YAG laser shown therein may bereplaced with a relatively low power laser, since no engraving isrequired of the reading optics 202. The read control/data acquisitionand processing section 206 controls the operation of the reading optics202 and receives and processes signals provided through the readingoptics section in a manner similar to the control system 114 and thesignal processing section 106 shown in FIG. 2A, so that the section 206shown in FIG. 4 may be embodied in accordance with the control system114 and the signal processing section 106 shown in FIG. 2A. On the basisof the reading operation, the binary serial number represented by thecode pattern 22 is read by the processing section 206, and then apredetermined encryption algorithm is performed with respect to themachine-readable serial number to provide an encrypted serial numberthat is to be applied in human-readable form on the disk 10. Signalsrepresenting the encrypted serial number are provided to the engravingcontrol section 208, which controls the engraving optics section 204 sothat the encrypted serial number is engraved in the form ofalpha-numeric characters on disk 10, and preferably in the hub area 12thereof. The engraving optics section 204 and the engraving controlsection 208 may take the form of conventional equipment used forengraving identification code symbols on CD-ROMs. In a preferredembodiment of the invention, the engraving optics section 204 includes aconventional laser cutting device such as a CO₂ laser.

Although it is preferred to apply the encrypted human-readable serialnumber by engraving, it is also within the contemplation of theinvention to apply the human-readable number in the form of ink, eitherdirectly on the surface of the disk 10, or on a label that adheres tothe disk 10. In both cases, the human-readable number is preferablyapplied in the hub area 12.

It is also within the contemplation of the invention that, for thepurpose of applying the human-readable serial number, themachine-readable code pattern be read using apparatus and procedures asdescribed below in connection with FIGS. 5 and 7.

FIG. 5 is a schematic illustration of a system 220 by which themachine-readable serial number on a disk 10 may be read in connectionwith a software package unlocking operation in accordance with thepresent invention. The system 220 may be made up of a conventionalpersonal computer 222 to which a conventional CD-ROM drive 224 isconnected as a peripheral device. To carry out the software unlockingoperation to be described below, appropriate software in accordance withthe invention is loaded into the PC 222 to control the operation of thesystem 220 for software package unlocking. For example, the softwareneeded for the unlocking operation may be stored in unlocked form on thedisk 10 and loaded into the PC 222 by way of the CD-ROM drive 224.

As previously indicated, the CD-ROM 10 preferably contains a largenumber of software packages, perhaps 100 or more, of which at least someare "locked" such that access to the packages can only be obtained ifrespective access codes are entered into the computer in which thepackages are to be installed. Also, the disk 10 includes themachine-readable serial number code 22 (FIG. 1B) and a human-readableencrypted serial number applied as discussed above in connection withFIG. 4. If a customer desires to obtain access to one of the lockedsoftware packages on the disk 10, the customer reads the human-readableencrypted serial number from the disk and contacts the distributor ofthe disk. The customer provides the encrypted serial number to thedistributor and indicates the software package which he desires toaccess, and also makes payment arrangements or the like. The distributorcarries out a decryption algorithm with respect to the encrypted serialnumber provided by the customer in order to determine the serial numberrepresented by the code pattern 22 on the disk 10 held by the customer.On the basis of the serial number represented by the code 22 of theparticular disk 10 and a code representing the software package to beunlocked, an encryption algorithm is performed to produce an access codefor unlocking the program from the particular disk 10 held by thecustomer. After confirming the payment arrangements, etc., thedistributor communicates the access code to the customer. It will beappreciated that the communication between the customer and thedistributor may include mail, data communication, oral conversation viatelephone, or a combination thereof.

FIG. 6 is a flow chart which illustrates a software routine carried outby the system 220 to unlock the desired software package on the disk 10using the access code received by the customer from the distributor. Theroutine begins with a step 300, at which the customer, perhaps inresponse to an appropriate prompt, enters information, via keyboardentry or the like, which indicates the software package on the disk 10which is to be unlocked. Step 302 then follows, at which the access codereceived from the distributor is entered, again perhaps by keyboardentry in response to a prompt.

If the disk 10 has not already been inserted in the CD-ROM 224, thesystem 220 prompts the customer to do so and then the system 220proceeds to perform a sub-routine (represented by step 304) in which theserial number code pattern 22 on the disk 10 is read in a manner to bedescribed in detail below. The routine of FIG. 6 then proceeds to step306 at which the system 220 performs a decryption operation with respectto the access code entered by the operator to produce decryptedinformation which, if the access code is valid, will match the serialnumber read by the system 220 from the disk 10 as well as a coderepresenting the software package to be unlocked. Alternatively, anencryption algorithm may be performed with respect to the serial numberread by the system 220 at step 304 and the code indicative of thesoftware package to be unlocked, and the result of the encryptionalgorithm is compared with the access code entered at step 302. In thiscase, the access code is considered to be valid if it matches the resultof the encryption of the serial number and the software package code.

The routine of FIG. 6 branches at step 308, depending upon whether theaccess code was found to be valid. If so, the routine proceeds to step310, at which the desired software package is unlocked by, for example,loading the software package from the CD-ROM 10 into the PC 222 so thatthe customer has access to the desired package. On the other hand, ifthe access code was found not to be valid, the routine branches fromstep 308 to step 312, at which an error message or the like is displayedindicating that the access code is invalid, access to the desiredpackage will be denied, etc.

FIG. 7 is a flow chart which illustrates the subroutine for reading thecode pattern 22 represented by step 304 of FIG. 6. The sub-routine ofFIG. 7 begins with a step 350 at which a bit counter is initialized, tothe value "1" for example, and the routine then proceeds to step 352, atwhich the system 220 attempts to read specific predetermined storagelocations on the disk 10 which correspond to the bit represented by thecurrent value of the bit counter. The storage locations which are to beaccessed at step 352 are all located in the engraving area 157 includedin the band 150 for the bit represented by the current value of the bitcounter. The address locations to be accessed with respect to each bitare sufficiently numerous, and are distributed within the engraving areafor the corresponding band 150 in such a manner, that at least some ofthe address locations coincide with locations from which the reflectivecoating has been removed if the bit corresponding to the particular band150 has the value "1", so that the addressing information is destroyedor unreadable and the address location cannot be accessed. Accordingly,and assuming the bit has the value "1", when it is attempted to read theaddress locations corresponding to the engraved spots or band, the PC222 returns an error message indicating that there is a defect in thedisk at the address location.

It is then determined at step 354 whether the number of defectiveaddress locations found at step 352 exceeds a predetermined thresholdnumber. If so, it is determined that the value of the bit represented bythe bit counter is "1" (step 356). However, if no defects are found, orthe number of defects is less than the predetermined threshold, then thecurrent bit value is set to "0" (step 358).

Accordingly, it will be seen that the value of the bit represented bythe bit counter is determined by detecting the presence or absence ofdefects intentionally formed on the disk 10 by removing the reflectivecoating to prevent reading of address information. The determination ismade by taking advantage of the routines typically provided in thesoftware for operating the PC 222 and/or the CD-ROM drive for detectingdisk defects.

Following step 356 or step 358, as the case may be, is step 360, atwhich it is determined whether the bit counter represents the last bitof the machine-readable code. If not, the routine proceeds to step 362,at which the bit counter is incremented and the routine then returns tosteps 352-358 for determining the value of the next bit. The routinecycles through steps 352-362, thereby reading the code pattern 22 bit bybit on the basis of the presence or absence of defects in the respectiveengraving areas 157 of the bands 150, continuing until the last bitvalue has been determined. At that point, the code has been completelyread, so that step 364 follows step 360.

In a preferred embodiment of the invention, the bands corresponding tothe code bits are accessed proceeding radially inwardly from theoutermost band or proceeding radially outwardly from the innermost band.However, it is also contemplated to read the bands in a scrambled order,and the writing operations previously described may also be performed ina radially inward, radially outward or scrambled order.

In the writing operations previously described, the defects formed tocreate the "1" bands were created by vaporizing the reflective coatingin selected areas. However, it is also within the contemplation of theinvention to form the defects in another manner such as adding anopaquing material at selected areas, or causing a chemical change on orbelow the surface of the disk which adversely affects reflectivity ofthe coating, so that in any of these cases defects are formed inaddressable locations by rendering the addressing informationunreadable, or the like.

In a preferred embodiment as described above, a 16 bit binary code wasformed as the machine-readable serial number. It may, however, beadvantageous to fix the value of one of the bits, e.g. by setting afirst (innermost or outermost) bit value to "1" to serve as a sync bitfor reading purposes, in which case the effective number of uniqueserial numbers would be reduced from approximately 64,000 toapproximately 32,000 . Even if the number of disks to be serializedexceeds 64,000 or 32,000, as the case may be, it is believed that eitherquantity of distinct serial numbers is sufficiently large to provideadequate security for the access codes. Nevertheless, if desired, thenumber of bits in the machine-readable code can be increased so that aunique serial number is provided for every one of the disks.

In the format described with respect to FIG. 3, the 16 bit code isformed in an annular area of about 1.6 mm in width, which occupiesapproximately 6.6% of the disk's information storage capacity. It willbe noted that the code bands formed by removing the reflective coatingare formed on a large scale as compared to the information storagetracks, which are typically at a pitch of about 1.6 microns, as comparedto the approximately 25 micron width of the code bands. Moreover, thewriting methods described above are not designed to place the codepattern area 20 at any particular predetermined position along thecircumference of the disk 10, so that the entire annular region in whichthe code pattern area might fall must be reserved. For most applicationsthe reduction in storage space caused by reserving the entire annularregion is not significant. However, it is also within the contemplationof the invention to provide more precise placement of code pattern bands24, or to replace the bands with isolated spots at particular locations,by providing more precise positioning of the engraving laser beam withrespect to the addressable storage locations of the disk 10. This may bedone, for example, using a modified version of a conventional CD-ROMdrive, in which the low power reading laser is replaced with a higherpower laser that can be selectively operated in a low power mode forreading an addressable location at which the laser beam is directed anda high power mode for creating a defect at that particular point. Inthis embodiment, the addressing information on the tracks of the disk 10can be read in order to position the laser at desired spots at whichdefects are to be created.

Although the invention has been described primarily with reference toserializing of CD-ROMs, it will be understood that the invention is alsoapplicable to CDs containing audio and/or video information or othertypes of information in addition to or instead of computer programs.Moreover, the invention is applicable to optical storage disks in avariety of formats, including the so-called "MiniDisc" format. Althoughthe invention is particularly useful with respect to optical storagedisks that are molded in large numbers from a single master, theinvention is also applicable to disks manufactured in other ways,including magnetic or magneto-optical recording.

Having described specific preferred embodiments of the present inventionwith reference to the accompanying drawings, it is to be understood thatthe invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein by one skilledin the art without departing from the scope or spirit of the inventionas defined in the appended claims.

What is claimed is:
 1. A method of reading a machine-readable code beingformed of a first plurality of bits recorded in a correspondingplurality of recording areas on a recording medium, said methodcomprising the steps of:determining a plurality of defect count valuescorresponding to said plurality of recording areas, wherein each one ofsaid plurality of defect count values corresponds to a number of defectspresent in a corresponding one of said plurality of recording areas;assigning a first predetermined bit value to respective ones of saidplurality of recording areas having a corresponding defect count valueexceeding a predetermined threshold; and assigning a secondpredetermined bit value to respective ones of said plurality ofrecording areas having a corresponding defect value less than saidpredetermined threshold, wherein said machine-readable code correspondsto the bit values assigned to said plurality of recording locations. 2.A method according to claim 1, wherein said recording medium comprises aCD-ROM, and wherein said determining step and said assigning steps areperformed using a CD-ROM drive interfaced to a personal computer intowhich said CD-ROM is inserted.
 3. A method according to claim 1, whereinsaid defects comprise a plurality of predetermined defects intentionallyformed onto said recording medium.